Bacteriophages (phages) are the viruses that infect bacteria as distinguished from animal and plant viruses. Phages can have either “lytic” or “lysogenic”life cycle.
Phages multiplying in a lytic cycle cause lysis of the host bacterial cell at the end of their life cycle. Temperate phages have the possibility of an alternative life cycle where they integrate their genomic DNA into the host bacterial chromosome so that this “prophage” is propagated passively by the bacterial chromosome's replication apparatus. Although largely inert and noninfectious prophages can, under some circumstances excise from the host genome, replicate in the lytic mode, produce numerous progeny and finally cause lysis of the host bacterium.
The natural capacity of phages to infect and subsequently efficiently kill bacteria, together with the enormous specificity of the phage-bacterial interactions, is the basic biological phenomena on which phage therapy is founded. Those phages that lack the capability to enter the alternative lysogenic life cycle, the so-called virulent phages, are the most suitable type of phage to employ for therapy.
Phage therapy was first proposed by D'HERELLE (The bacteriophage: its role in immunity; Williams and Wilkens Co; Waverly Press Baltimore USA, 1922). Although offering much initial promise as a effective means to treat diseases caused by bacterial infections, its therapeutic value remained controversial. Once antibiotic therapy became the treatment of choice for bacterial infections in the 1940s, little further attention was paid to phage therapy. The ultimate reason for this marked lack of enthusiasm for phage therapy was that no simple and reliable formulation of a efficacious bacteriophage composition emerged, i.e., one that is sufficiently virulent, non-toxic, host-specific, and yet with a wide enough host range to be of practical use. As a consequence research on the therapeutic use of phage stagnated for many years.
The extensive use of antibiotics has led to an increase in the number of bacterial strains resistant to most or all available antibiotics, causing increasingly serious medical problems and raising widespread fears of return to a pre-antibiotic era of untreatable bacterial infections and epidemics.
The ability to easily sequence entire microbial genomes and to determine the molecular basis of their pathogenicity promises novel, innovative approaches for the treatment of infectious diseases, but “traditional” approaches are also being re-explored with increasing emphasis. One such approach is bacteriophage therapy, which is attracting renewed attention as a potential weapon against drug-resistant microbes and hard-to-treat infection (STONE; Science; vol. 298; p: 728-731, 2002).
With the development of molecular biology, phage received much attention because they proved to be easy and extremely useful as model systems for fundamental research. Today phages are widely used in numerous molecular biology techniques (e.g., the identification of bacteria strains) and good laboratory procedures are available for the isolation of highly pure phage compositions.
The techniques of molecular biology can now also be applied to the field of phage. therapy. For example, WO 00/69269 discloses the use of a certain phage strain for treating infections caused by Vancomycin-sensitive as well as resistant strains of Enterococcus faecium, and WO01/93904 discloses the use of bacteriophage, alone or in combination with other antimicrobial agents, for preventing or treating gastrointestinal diseases associated with bacterial species of the genus Clostridium. 
US 2001/0026795 describes methods for producing bacteriophage modified to delay their inactivation by the host immune system, and thus increasing the time period in which the phage remain active to kill the bacteria.
US 2002/0001590 discloses the use of phage therapy against multi-drug resistant bacteria, specifically methicillin-resistant Staphylococcus aureus, and WO 02/07742 discloses the development of bacteriophage having an exceptionally broad host range.
The use of phage therapy for the treatment of specific bacterial-infectious disease is disclosed, for example, in US 2002/0044922; US 2002/0058027 and WO 01/93904.
However, commercial scale production of bacteriophage compositions and especially for therapeutic use is still a limiting factor. In current techniques, the titer of the phage composition is low, usually in the range of 109-1011 pfu/ml on a laboratory scale, and 107-109 on a commercial scale, whereas the titer typically required for phage therapy is greater than 1012 pfu/ml.
Additionally, to reach the desirable levels of phage titer, very large volumes of liquid phage infected bacterial cultures are required.
As described herein below, the dosage for phage therapy is in the range of 106 to 1013 pfu/Kg body weight/day, with 1012 pfu/Kg body weight/day suggested as a preferable dosage. According to the commonly liquid culture methods for phage production, attaining a phage yield equivalent to single daily dose of bacteriophage for a person would require a production volume of 5-10 liters. Commercial production of phage stock composition of one specific phage type would therefore involve the growth of cultures in a volume range of thousands of liters which even with large-volume fermenters would require multiple runs.
Such a large volume of liquid requires the use of large scale, and very expensive fermenters that are costly to operate and to maintain. Moreover, the subsequent processes of phage purification, at least in part, must also be performed with large volumes of liquid, making working under good manufacturing practice (GMP), necessary for the production of pharmaceutical compositions, very hard to achieve technically and economically.
In fact, a reasonable estimation of the cost for clinical trials in the field of phage therapy would be very high, one the reason being that the benefit of using a “cocktail” of different phages for effective treatment, would require that each phage be prepared separately in the special GMP facilities required for FDA approval. This implies, at least initially, that phage therapy would be relatively expensive.
Therefore, there is a recognized need for, and it would be. highly advantageous to have a method for the commercial production of phage compositions that increases the phage yield, reduces manufacturing volume so that proven, economical, small-volume purification processes can be applied to the obtained phage extract.